In an electronic apparatus, there are cases in which noise generated from electronic devices propagates through a parallel plate including a power supply and a ground plane that serves as a kind of waveguide so as to adversely affect other electronic devices or adjacent wireless circuits and the like. Therefore, in electronic apparatuses, it is normal to implement noise countermeasures, and a number of techniques have been developed.
In recent years, it has become evident that the propagation characteristics of electromagnetic waves can be controlled by disposing conductor patterns having a specific structure periodically (hereinafter described as a metamaterial). Particularly, a metamaterial configured to control electromagnetic wave propagation in a specific frequency zone is referred to as an electromagnetic band gap structure (hereinafter described as an EBG structure), and noise countermeasures using the EBG structure are attracting attention.
Examples of such techniques include a technique described in Patent Document 1 (specification of U.S. Pat. No. 6,262,495). FIG. 2 in Patent Document 1 shows a so-called mushroom-type EBG structure in which a plurality of island-shaped conductor elements are disposed above a sheet-like conductor plane, and each of the island-shaped conductor elements are connected to the conductor plane through a via hole.
In addition, Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2006-253929) discloses an EBS structure in which an intermediate layer having an inductance element such as a spiral inductor disposed between a patch layer and a conductor plane layer is provided, and the patch, the inductance element, and the conductor plane are connected through a via hole in FIG. 12. The above structure enhances the inductance component without enlarging the EBG structure so as to match the band gap zone to a low-frequency zone.